The U.S. Environmental Protection Agency (EPA) estimates that approximately 250 million scrap tires are generated in the United States each year. In the United States alone, the Rubber Manufacturers Association (RMA) has estimated that between two and three billion scrap tires currently reside in landfills or are otherwise stockpiled. Waste tires take up a significant amount of space in landfills, and burying of the tires can lead to landfill contamination. Stockpiling waste tires provides breeding grounds for pests and represents a significant fire hazard. Burning of tires causes a significant amount of air pollution, and run-off from tire fires can contaminate ground water. The handling and disposal of waste tires is a significant environmental problem, and the desirability of recycling waste is evident.
One method of recycling waste tires is pyrolysis. Known tire pyrolysis processes include heating tires to produce useful products such as oils, gases, recyclable metals, and carbonaceous char. As disclosed in U.S. Pat. Nos. 5,783,046, 6,372,948, and 7,037,410 to Flanigan, the entire disclosures of which are hereby incorporated herein by reference, a known pyrolysis process includes heating rubber in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distilling a vapor comprising hydrocarbon from the rubber, and producing a solid carbonaceous char. Weinecke et al. in U.S. Pat. No. 7,101,463, hereby incorporated herein by reference in its entirety, describes a system and process for the recovery of oil from shredded vehicle tires that utilizes a pair of sequentially positioned packed towers. Also disclosed in U.S. Pat. No. 5,894,012 to Denison, hereby incorporated herein by reference in its entirety, is a waste processing system that produces clear and colorless oil for use in rubber and plastic applications and a carbonaceous char equivalent to a low structure furnace black.
The carbonaceous char produced from typical pyrolysis processes is generally a friable material. The carbonaceous char can be reduced to finely-divided particles or “fluff” form through known pulverization techniques. However, a mixing and dispersion of finely-divided particles of carbonaceous char into rubber and plastics is known to be problematic.
A variety of methods for converting individual particles of carbon black into pellets for improved mixing and dispersion are known to the art. For example, a finely-divided carbon black may be agitated under dry conditions in such a manner as to reduce the quantity of air or other gases associated with the carbon black and cause a degree of agglomeration of the discrete particles of the carbon black. Under wet conditions, the finely-divided carbon black may be agitated in a wet pelletizer in the presence of sufficient liquid pelletizing medium, such as water or a dilute aqueous solution of a binder such as sugar, molasses, dextrin, starch, calcium lignin sulfonate, and the like, to permit agglomeration of the individual particles into free-flowing pellets of suitable structural strength and stability. However, the application of standard carbon black dry and wet pelletization techniques to carbonaceous char from pyrolysis processes has not provided a desirable pelletization quality.
There is a continuing need for a system and method of converting a carbonaceous char from a pyrolysis process to a free-flowing pelletized form in order to permit inexpensive and convenient handling, storing and shipping thereof. Desirably, a carbon black product produced from the carbonaceous char is provided in a form convenient for use by manufacturers of rubber, plastics, and other commercial products.